You can upgrade your bomb carrying capacity twice. To get the first, you must go to Goron City. Find the Goron that's rolling around the city in a loop, and detonate a bomb near enough to make him stop. To get the second, you must beat the Bombchu Bowling Alley in Castle Town. Since the prizes for winning are randomized, you'll have to keep beating the challenge until you win the upgrade.

If you have to cross Hyrule Field at night, equip the Bunny Hood. As long as you have it on, the Stalchildren won't appear.

If you touch a butterfly with a Deku Stick, it'll transform into a fairy.

NOTE: There is always a possibility your game data can be corrupted, so do this at your own risk!

Start a game in the Temple of Time, then gently and SLOWLY pull up on the left side of the game cartridge. If you do it slow enough, the computer will become lagged, Link will jump all over the screen, and the sound will become very corrupted. If you let this happen for a few seconds, the N64's processor will become lagged and the game will lock up; there's going to be a small yellow bar that will appear in the top-left of the screen. When you get the small yellow bar to appear, there are some commands that you need to input on the controller to get the "debug" code to appear on the screen. This will also show the time and date that your particular game was made. Enter these button combos to make the code appear onscreen:

1: L + R + Z
2: Control Pad Up + C-Down
3: C-Up + Control Pad Down
4: Control Pad Left + C-Left
5: C-Right + Control Pad Right
6: A + B + Start

The debug/error code won't be shown unless you push each button listed. Example: in the first step, you must push the Z button while HOLDING the L and R buttons.

You can upgrade your Deku Nut carrying capacity twice. Both upgrades are located in the Lost Woods. The first upgrade can be purchased for 40 rupees from a Business Scrub hidden in the underground grotto near the Sacred Forest Meadow. The second can be obtained by equipping the Mask of Truth and speaking to the Deku Scrub on the far right side of the Forest Stage. Note that due to a glitch, this second upgrade must be obtained before acquiring the Poacher's Saw.